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SIG Sauer Custom Works P320 Handgun: Select Your Configuration

The SIG Sauer concierge service lets you build the P320 of your dreams. Handguns did just that. Here's the feature set we selected and why.

SIG Sauer Custom Works P320 Handgun: Select Your Configuration

The SIG Sauer P320 is arguably the most successful striker-fired design the U.S. market has seen in the past decade. After all, a gun doesn’t get chosen to replace a longstanding U.S. service pistol—as the P320, in its M17 and M18 guises, did in 2017 when it supplanted the Beretta 92/M9—if it doesn’t have a lot going for it. And it’s particularly impressive when you realize the P320 was SIG’s first striker-fired pistol.

The P320 is currently available in two dozen configurations, with about every feature you could think of. But what if none of these is exactly what you are looking for? SIG has a solution for that: Build your own, through its concierge service.

SIG kindly extended an offer for Handguns to do exactly that, and the resulting Custom Works gun received a star turn on last season’s “Handguns & Defensive Weapons.”

The process couldn’t be simpler. Just visit and search for the “Build Your Own P320” link. Click on that, and you’ll be asked to register with your email address and a password. And then the fun starts.

It all begins with the Custom Works 320 FCU (Fire Control Unit). It features a skeletonized, flat-face trigger and a gold titanium nitride finish. In previous articles on P320 series pistols, reviewers had called out the gun for its heavy trigger pull. Not with the 320 FCU. At three pounds, four ounces on average, it’s definitely not heavy.

SIG Sauer Custom Works P320 Handgun Two-Tone Look
Rupp went with a two-tone look, a black slide contrasting with the titanium Cerakote finish on the alloy grip module. It blends nicely with the black/gray grip panels and is set off by the gold trigger.

It’s not the crispest striker-fired trigger I’ve ever shot, as it has some creep and is a wee bit spongy. But between the light weight and the flat face that encourages a straight-back trigger press, I think it’s a good one.

The P320 is a modular pistol, and the FCU is the serialized part. This allows you to change grip modules, slides and even chamberings while retaining the same serial number. The number is visible through a cutout in the grip module, just below the right-side slide-lock lever. In the case of the Custom Works guns, you’ll see the special FCU serial number prefix.

Again, the FCU is the common starting point for the build. From here the world is your oyster. SIG’s Michael Marotte suggested I go with the Carry size, which suits me because I love the middle road. The Carry size sits between the 320’s Full-Size and Compact versions.

For the grip module, I chose the AXG for a couple of reasons. AXG, which stands for Alloy X-Series Grip, is aluminum versus the standard-issue polymer. There’s nothing wrong with polymer-frame semiautos—I own several—but I do prefer metal, and an alloy frame results in a gun that’s more controllable while still being light enough to carry.

SIG Sauer Custom Works P320 Fire Control Unit
The Custom Works 320 FCU has a gold titanium nitride finish and a flat, skeletonized finger lever. Trigger pull weight was excellent.

For years I struggled with SIG pistols because their grip styles never suited me. That’s one of the things SIG changed in the X-Series P320s, providing a less chunky grip and a grip angle that’s closer to the 1911. It’s not exactly undercut behind the trigger guard, but it is relieved there, and overall it fits me well. A minor change you may notice is that the AXG frames employ a rounded magazine release, as opposed to the triangular release that is the hallmark of other P320s.

The AXG grip module is available in black, flat dark earth and, my choice, a titanium Cerakote finish that I chose for purely aesthetic reasons. All told, the AXG frame added $400 to the base price at the time, but the AXG frames are currently listing at $300. Your other choices are the titanium-infused polymer TXG ($250) and various polymer frames ($90).

I should note that as you drag your cursor over the various choices, an image of how the gun will look changes. When you make a selection and move to the next component, your gun shows on the screen as it’s currently configured. So at this point in the build process, on my computer screen I’m seeing the gold FCU housed in the titanium-finished AXG grip module, and I’m happy.


Next up is grip panels, and here is where you can really make your pistol stand out—or not. I went with a simple black/gray G10, but you can select G10 finishes in walnut or a veritable rainbow of color patterns—as well as several options from well-respected maker Lok Grips. Grip options tack on between $115 and $170, with my choice adding $120.

SIG Sauer Custom Works P320 Barrel
Rupp opted for a 4.6-inch threaded barrel on the 3.9-inch X-Series slide. Customized slide engravings on the left and right—“HANDGUNS” in this case—really personalize the pistol.

There’s a lot to consider when it comes to slides, and the system prevents you from making incompatible choices. Lengths include 3.6, 3.9 and 4.7 inches, and there are black, coyote tan and stainless finishes as well as different slide styles. As to the latter, you can select from the unique Spectre to the race-gun-looking Pro-Cut in addition to more basic slides.

I opted for simple here and chose an X-Series in plain ol’ black and the 3.9-inch length. It comes with suppressor-height sights in the excellent X-Ray 3 day/night configuration: twin tritium lamps on either side of the rear notch and a tritium lamp surrounded by a high-visibility green dot on the front blade.

Slide charges run from $280 for the standard slide to $450 for the Pro-Cut and Spectre. My choice added $350 to the bill.

Barrels come next, and as configured, I was presented with only a few choices—the main being to go the threaded-barrel route or a plain barrel. I went with threaded ($230), 13.5x1 left-hand threading. The 1/2x28 pattern is also an option. It’s a 4.6-inch barrel, necessarily being longer to accommodate the threaded portion. Standard 3.9-inch barrels are available in black ($180) or gold ($230) finish.

You don’t get a choice on recoil assembly, as it must match the slide/barrel length you’ve already chosen. In the case of the 3.9-incher I built, it’s $40.

Magazines are another matter. If you live in a restrictive state, as I do, your options shrink, but they still exist. You can go with the basic 10-rounder ($50), which is a standard mag that’s “dimpled” so it won’t accept more than 10 cartridges. For another $10 you can select a Legion mag, which sports a bumper with the Legion logo.

SIG Sauer Custom Works P320 Rear Sight
Suppressor-height X-Ray 3 day/night sights—tritium lamps in the rear and a tritium/green dot front—pair up with a SIG Romeo 1 slide optics cut.

In the standard-capacity realm, you can opt for 17- or 21-round magazines, in black or coyote. These are $50 as well, except for the 17-round Legion, which again comes with a $10 upcharge.

All slides are cut for optics, and you also have the option of having the gun ship with a SIG Romeo 1 Pro in either three or six m.o.a. I didn’t add this, but if I had, it would run $440.

And since you’ve gone through this process to build a pistol with your personal stamp on it in terms of features and looks, it only makes sense to get an extra personalized touch. The final step in the build is engraving, provided at no charge. You can get different lettering engraved on the left and right sides, or you can do as I did and have them the same. Both engravings are limited to 20 characters.

There’s even a font choice: Arial or Garamond. As an old print guy, I could go on and on about fonts, but I won’t. Just experiment by typing in your choices in the boxes and then switching fonts back and forth to judge them on the screen.

If at any time during the process you get a little lost or you think your build has gotten out of hand, you can reset to the base configuration. When you’re satisfied with your selections, click on “Submit Build Request.” Not long afterward, a friendly SIG company representative will give you a call to go over your order. They will review with you each selection to ensure you’re getting exactly what you want.

Turnaround time is four to six weeks. When your pistol arrives, it shows up in a combo-lockable hard case with a fitted foam liner and three magazines. You also receive a cool SIG challenge coin. It has a pewter SIG logo on one side and an American-flag themed “Live Free or Die” (New Hampshire’s state motto) Custom Works logo on the other.

I was definitely not disappointed when my pistol arrived. It’s a handy, all-around pistol that looks terrific. In my opinion, my understated aesthetic picks not only work well together, but also they show off the gold FCU for a classy pistol.


How does it shoot? The company sent along a test target that has a three-shot group with all bullet holes touching. I’m assuming that comes from a machine rest, and I certainly wasn’t able to duplicate anything close to that off a benchrest at 25 yards with the iron sights, as you can see in the accompanying accuracy chart.

However, in practical field shooting the gun really shines. My TV co-hosts and I got a good deal of trigger time with it on set, and I ran drills with it on my home range. It draws really nicely from the holster and gets on target quickly.

The weight and balance are outstanding. It’s easy to track the sights through recoil, and they come back on target fast. I’d tested the M18 version of the P320 a year or so ago, and my one criticism was the amount of muzzle flip. This Custom Works gun—which has essentially the same overall length—was a lot better in this regard, thanks to the alloy AXG grip module.

Breaking good shots is no problem thanks to the light, straight trigger pull. The magazine release is easy to activate, and mags drop free with no hang-ups. Speaking of controls, there is no manual safety. While the slide-lock lever looks like it’s on the small side, its design is such that it’s easy to use for locking the slide and as a slide release.

The G10 grip panels, which include a section on the backstrap, along with the serrations on the frontstrap keep the gun anchored in the hand.

The gun was utterly reliable. It never malfunctioned in my testing or on the TV show. Together with the M18 I shot, which was also completely reliable, I’ve come to appreciate why the P320 is so popular and why the military chose it. As built, the Custom Works gun was great on the range, and while it’s no micro 9mm, at 32 ounces it’s light enough and compact enough that I can carry it if I want to.

I still need to get a suppressor for it, and at that point, with a light/laser added to the gun’s three-slot accessory rail, it will become our primary home defense gun. Frankly, it’s why I went with the threaded barrel. Having a can on a home defense gun makes so much sense, as you won’t be subjected to the highly disorienting noise of gunfire in a closed environment.

Total cost on this particular P320 build was $1,570. A few component prices have changed since I did it, but there’s no denying it’s an expensive gun. You could trim a couple of hundred bucks off that by making different choices, but if your goal is to have a pistol with the exact feature set you want—one that will fill you with some pride every time you look at it—SIG’s concierge service P320 is definitely worth investigating.

SIG Sauer Custom Works P320 Specifications

  • Type: Striker-fired semiauto
  • Capacity: 10+1 (tested), 17+1, 21+1
  • Barrel: 4.6 in., threaded 13.5x1 left-hand
  • OAL/Height/Width: 8.1/5.5/1.3 in.
  • Weight: 32 oz.
  • Construction: Nitron-finished stainless steel slide; titanium Cerakote-finished AXG alloy grip module
  • Grip Panels: Black/gray G10
  • Trigger: Custom Works 320 FCU; gold titanium nitride finish; flat, skeletonized finger lever; 3 lb., 4 oz. pull (measured)
  • Safety: Striker, Disconnect
  • Price: $1,570 (at time of build)
  • Manufacturer: SIG Sauer,

SIG Sauer P320 Assembly/Disassembly Tips

The P320 was designed to be incredibly safe to disassemble. For one, you have to eject the magazine, otherwise you can’t rotate the takedown lever. Yes, dropping the mag should always be the first step to unloading or disassembling any pistol, but here you have no choice if you’re going to take it apart. Second, it’s not necessary to pull the trigger to remove the slide/barrel.

There are a couple of tricks to reassembly, and one applies to the Carry, Compact and Subcompact models. At the rear of the recoil spring guide assembly you’ll see two flats with small holes. The flat/hole side must be positioned vertically in order to reassemble.

The second applies to all P320s and involves the final step where you’re sliding the assembled slide back onto the frame. If you “cheat” and simply rotate the takedown lever without locking back the slide, the gun won’t function. You’ll get no trigger pull. You must lock back the slide with the slide-lock lever. Once you’ve done so, you can rotate the takedown lever to its horizontal position and you’re good to go.

If you want to remove the fire-control unit to swap out a grip module, the manual says pull out on the takedown lever while rotating it. At least the first time you do this you’re going to need to use some force. Just wiggle and pull hard until it comes out. Then push forward on the fire-control unit and tilt up to remove.

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